Process of removing viscous oil from a well bore



Jan. 14, 1958 J. L. P6PHAM ETAL 1 PROCESS OF REMOVING VISCOUS OIL FROM A WELL BORE Filed Jan. 19, 1956 IIQVENTORS ,1 1.. POPHAM 0. 4. SHOCK ATTORNEY PROCESS OF REMOVING VISCOUS OIL FROM A WELL BORE lack L. Popham and DArcy A. Shock, Ponca City, Okla, assignors to Continental Oil Company, Ponca City, Okla, a corporation of Delaware Application January 19, 1556, Serial No. 560,171

9 Claims. (Cl. 166-39) This invention relates to an improved process of recovering viscous oil from subsurface strata, and more particularly, but not by way of limitation, to an improved process of recovering viscous oil by utilizing a combination heat and gas drive. For the purpose of this specification and the appended claims, vsicous oil may be defined as liquid hydrocarbons entrained in any type of strata and not naturally flowable into a well bore trav ersing the strata.

In one aspect, this invention relates to what is commonly known as secondary recovery of oil which will not normally flow into a well bore, such as the heavy crude in sands, or oil in tar sands. Various methods of secondary recovery by the use of heat and/or gas drive have been proposed, but, to the best of applicants knowledge, none have proved economically feasible. One general type of such methods involves the circulation of a heated fluid, such as oil, gas or steam through the lower portion of a well bore in contact with a formation containing the entrained oil. Perhaps the greatest deficiency of these methods is the lack of penetration of heat through the formation. Ordinarily, only the formation in the immediate proximity of the well bore is effectively heated to reduce the viscosity of the oil and induce the oil to flow into the well bore.

Another type of proposed secondary recovery method utilizes two or more spaced well bores. In general, combustion is initiated in one well bore and driven through the formation to an adjacent well bore. In rather ideal formations, Where the formation is sufficiently permeable to permit pumping gas from one well to another, and where the well bores are closely spaced, such methods are effective in recovering a large portion of the oil which will not normally flow into the well bores. However, the use of two well bores unduly increases the cost of the method, and in many formations it is extremely diflicult to establish gas communication between the wells.

This invention is also useful in the removal of oil from oil shale. Present known methods for this purpose ordinarily involve the formation of horizontal tunnels through the shale, with or without interconnecting channels. Hot gas or an absorbent is circulated through the various passageways to heat the shale in the immediate vicinity of the passageways and provide a drainage of oil into the passageways for subsequent removal. It will be apparent that the formation of the passageways is an extremely expensive operation and only the oil in the immediate vicinity of the passageways is removed.

The present invention contemplates a novel process for removing viscous oil from a strata or formation through the use of a single well bore. Combustion is initiated in the top portion of the strata around the well bore, and the resulting flame front is moved downwardly around the well bore to progressively heat the strata. As the strata is heated, the entrained oil becomes less viscous and flows into the lower portion of the well bore ahead of the flame front. The movement of the oil is assisted by a gas drive 2 consisting of the products of combustion from the flame front and air forced through the strata to support the combustion but not used in the combustion process.

An important object of this invention is to provide an economical process of removing viscous oil from subsurface strata.

Another object of this invention is to provide an improved process of removing viscous oil from subsurface formations by utilizing a single well bore.

Another object of this invention is to provide a process utilizing a combination heat and gas drive for removing viscous oil from around a single well bore.

A further object of this invention is to provide a maximum recovery of oil from around a well bore.

Another object of this invention is to remove viscous oil from a subsurface strata through a substantial distance around a well bore.

A still further object of this invention is to provide a downward flow of heat through an oil-bearing formation surrounding a well bore.

Other objects and advantages of the invention will be evident from the following detailed description, when read in conjunction with the accompanying drawing which illustrates our invention.

in the drawing, the single figure is a vertical sectional view through a well bore illustrating (partially schematically) one form of apparatus which may be used in practicing this invention.

Stated broadly, the present invention may be defined as a process of removing viscous oil from a subsurface strata traversed by a vertical well bore, including the steps of:

(a) Initiating combustion in the upper portion of the strata around the well bore to form a flame front, and

(b) Continuously forcing gas into the upper portion of the strata for feeding the flame front and forcing the flame front downwardly around the well bore, whereby the strata is progressively heated in a downward direction and the products of combustion are forced downwardly to release oil entrained in the strata and direct the re leased oil into the well bore at the lower portion of the strata.

Referring to the drawing in detail, reference character 2 designates a well bore extending downwardly from the surface 4 through formations 6 and 8 and terminating in a lower formation 10. It will be understood that the well bore 2 will actually extend through a plurality of subsurface formations and that only two of such formations are shown for simplification. The formation or strata 8 may be any type of oil-containing material where the oil will not normally flow into the well bore 2, such as an oil sand containing heavy crude, or an oil shale.

A well casing 12 extends downwardly through the well bore 2 and terminates at a point above the lower formation 10 Within the lower portion of the oil-bearing formation 8. The upper end 14 of the casing 12 is capped or closed off above the surface 4, and a conduit 16 communicates with the casing 2 above the surface for purposes which will be hereinafter set forth. Three strings of tubing, 18, 20 and 22, are disposed concentrically in the casing 12. The outer tubing string 18 terminates slightly below the lower end of the casing 12, and the upper end 24 of the tubing 18 is capped or closed off around the next smaller tubing string 20. A conduit 26 communicates with the upper end portion of the tubing 18 above the upper end 14 of the casing 12.

The middle-sized tubing string 20 extends downwardly through the tubing 18 and preferably terminates in proximity with the lower end 28 of the well bore 2 for posihereinafter set forth. The upper end 30 of the tubing Patented Jan. 14, 1958 20 extends above the tubing 18 and is capped around the smaller tubing 22. Also, a conduit 32 communicates with the tubing string 20 above the upper end 24 of the tubing 18.

The smaller tubing string 22 extends downwardly in the tubing string 20 to a depth approximating the depth of the tubing 20, and the upper end 34 of the tubing 22 extends outwardly to receive air or gas as will be more fully hereinafter set forth.

In practicing the present invention, the casing 12 is cemented to the walls of the well bore 2 through the central portion of the oil-bearing formation 8 as indicated by reference character 36. Thus, the formation 8 is in direct communication with the casing 12 throughout the upper portion of the formation, and the formation is in direct communication with the large tubing string 18 through the lower end portion of the formation. It is preferred that the cement 36 extend through the major portion of the formation 8 to provide relatively small exposed portions of the formation above and below the cement 36.

A plurality of perforations 38 are formed in the casing 12 above the cement 36 and opposite the upper portion of the oil-bearing formation 8. Also, a suitable packer or concrete ring 40 is preferably disposed between the outer surface of the casing 12 and the walls of the well bore 2 above the perforations 38 adjacent the upper end of the oil-bearing formation 8.

In one embodiment of this invention a horizontal fracture 42 is formed in the upper portion of the oil-bearing formation 8 opposite the perforations 38. Also, one or more fractures may be formed in the lower portion of the formation 8 below the lower end 46 of the casing 12. These lower fractures may be either horizontal (as shown at 44) Or vertical (as shown at 45) fractures. After the fractures 42 and 44 or 45 have been formed and the casing 12 is set in the well bore 2 as illustrated in the drawing, the tubing string 18 is run inside the casing 12 and a packer 48 is set between the tubing 18 and the casing 12 opposite the cement 36.

Air is then forced through the conduit 16 downwardly through the annulus between the casing 12 and the tubing 18 and then outwardly through the perforations 38 into the upper horizontal fracture 42. The packers 40 and 48 and cement 36 direct the air into the perforations 38 and fracture 42. The oil in the fracture 42 may then be igmted by any suitable means and the air will supply the necessary oxygen to promote combustion. In some formatrons, the oil entrained in the formation 8 surrounding the fracture 42 will be ignited upon being contacted by the fresh a r discharging through the perforations 38.

As the high pressure air is supplied through the fracture 42, the flame front resulting from the combustion of the arr and the oil entrained in the formation 8 will proceed downwardly through the formation 8 around the well bore 2 in the direction indicated by the arrows. Also, the gases of combustion will be forced downwardly through the formation 8 by the high pressure incoming air and will re-enter the well bore 2 below the lower end 46 of the casing 12.

It will thus be apparent that the oil entrained in the formation 8 around the well bore 2 will be removed and directed into the lower portion of the well bore by a combination of two different effects. The heat of combustion will heat the formation 8 and reduce the viscosity of the entrained oil to induce a downward flow of the oil toward the lower portion of the well bore 2. In addition, the gases of combustion, along with a portion of the air not utilized in the combustion process, will provide a gas drive to force the entrained oil downwardly toward the lower portion of the well bore 2. The lower fractures 44 or 45 will facilitate flow of the entrained oil into the well bore.

The gases of combustion entering the lower portion of the well bore 2 will be discharged upwardly through the tubing string 18 and out the conduit 26; whereas the oil removed from the formation 8 will accumulate iuthe lower portion of the well bore 2 and may be removed by any desired artificial lifting means. However, in some formations the amount and pressure of the gas discharging into the lower portion of the well bore 2 may be suflicient to provide a removal of the accumulated oil along with the combustion gases through the tubing 18.

As previously noted, any desired artificial lifting means may be utilized to remove the oil accumulated in the lower portion of the well bore 2. For purposes of illustration we have shown, schematically, a gas lift arrangement comprising the tubing strings 2i and 22. Air or under pressure may be forced downwardly through the inner tubing 22 and discharged upwardly through the tubing string 20. As this high pressure gas reverses direction and proceeds upwardly through the tubing string 20 it will pick up a portion of the accumulated oil and provide a gas lift of the oil through the tubing string 20. The combined oil and gas is discharged through the upper conduit 32 to a suitable separator or the like (not shown).

Prior to initiating combustion in the upper fracture 42, it may be desirable to establish gas communication downwardly through the formation 8 around the Well bore 2. In that event, the high pressure air supplied through the perforations 38 will be forced downwardly through the formation 8 around the well bore 2 and the cement sleeve 36 into the lower portion of the Well bore 2, until a return of the air is noted through the outlet conduit 26. When this condition occurs the air and the oil entrained in the formation 8 may be ignited within the fracture 42 to start the downwardly moving flame front.

It will be noted that the packer or cement ring 40 prevents an upward flow of the air through the annulus between the casing 12 and the well bore 2 to direct the high pressure air into the fracture 42. Also, the fracture 42 will normally be formed below the interface 50 between the formations 6 and 8, whereby the interface 50 provides a barrier to an upward flow of air from the fracture 42 through the formation 6. Thus, the air will be constrained to flow in a generally downward direction from the fracture 42 through the formation 8. And since the lower portion of the well bore 2 will be at a lower pressure than any other accessible portion of the formation 8, the air (as well as the gases of combustion resulting from the flame front) will follow the path of least resistance and flow into the lower portion of the well bore 2.

The upper fracture 42 provides an extension of the flame front to a substantial distance from the well bore 2. The air introduced into the fracture 42 will completely fill the fracture to induce combustion all the way out to the outer limits of the fracture 42. The lower fractures 44 assist in the establishment of gas communication from the upper fracture 42 to the lower portion of the Well bore 2 and facilitate the flow of the heated oil into the well bore. It will be apparent, however, that in relatively permeable formations it will not be necessary to form the lower fractures 44 or 45, since gas communication will be easily established between the upper fracture 42 and the lower portion of the well bore 2.

From the foregoing it will be apparent that the present invention provides an economical process of removing viscous oil from subsurface strata. The process utilizes a single well bore and involves the use of a combination heat and gas drive for removing the viscous oil. The maximum amount of oil may be removed from a single well bore and the present process will reach the viscous oil a substantial distance from the well bore. The flame I front progresses downwardly around the well bore in the same direction as the gas flow to provide an efficient heat and gas drive.

While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover by the appended claims any such modifications as fall within the true spirit and scope of the invention.

The invention having thus been described, what is claimed and desired to be secured by Letters Patent is:

1. A process of removing viscous oil from a subsurface strata traversed by a vertical well bore, including the steps of: ((1) initiating combustion in the upper portion of the strata around the well bore to form a flame front, and (b) continuously forcing gas only into the upper portion of the strata for feeding the flame front and forcing the flame front downwardly around the well bore, whereby the strata is progressively heated in a downward direction and the products of combustion are forced downwardly to release oil entrained in the strata and direct the released oil into the well bore at the lower portion of the strata.

2. A process as defined in claim 1 characterized further in that the upper portion of the strata is horizontally fractured around the well bore and combustion is initiated in the fracture.

3. A process as defined in claim 1 characterized further in that the upper and lower portions of the strata are fractured around the well bore and combustion is initiated in the upper fracture.

4. A process as defined in claim 1 characterized further in that gas communication is established from the well bore at the upper portion of the strata downwardly through the strata around the well bore and back into the well bore at the lower end of the strata prior to initiation of combustion.

5. A .process as defined in claim 1 characterized further in that the lower portion of the strata is vertically fractured around the well bore prior to the initiation of combustion.

6. A process of removing viscous oil from a subsurface strata traversed by a vertical well bore, including the steps of: (a) placing a casing in the well bore at a depth where the casing terminates in the lower portion of the strata, (b) cementing the casing in the well bore from the lower end of the casing through the major portion of the strata, (c) perforating the casing opposite the upper end portion of the strata above the cement, (d) suspending a tubing in the casing, (e) packing the tubing to the casing below the perforations in the casing, (1) forcing air down through the annulus between the tubing and casing, outwardly through the perforations, downwardly through the strata around the well bore, and back into the well bore and the lower end of the tubing, and (g) initiating combustion of the air and the oil in the strata at the upper end portion of the strata to form a flame front around the well bore, whereby the air feeds and forces the flame front progressively downward around the well bore to heat the strata and drive oil from the strata into the well bore at the lower end portion of the strata.

7. A process as defined in claim 6 characterized further by including the step of horizontally fracturing the strata around the well bore opposite the perforations in the casing prior to the initiation of combustion.

8. A process as defined in claim 6 characterized further by including the steps of horizontally fracturing the strata around the well bore opposite the perforations in the casing, and fracturing the strata around the well bore below the lower end of the casing.

9. A process as defined in claim 1 characterized further by including the step of removing the released oil from the well bore upwardly through the well bare to the surface.

References Cited in the file of this patent UNITED STATES PATENTS 1,457,479 Wolcott June 5, 1923 2,675,081 Nowak Apr. 13, 1954 FOREIGN PATENTS 481,151 Canada Feb. 12, 1952 

1. A PROCESS FOR REMOCING VISCOUS OIL FROM A SUBSURFACE STRATE TRANSVERSED BY A VERTICAL WELL BORE, INCLUDING THE STEPS OF: (A) INITIATING COMBUSTION IN THE UPPER PORTION OF THE STRATA AROUND THE WELL BORE TO FORM A FLAME FRONT, AND (B) CONTINUOUSLY FORCING GAS ONLY INTO THE UPPER PORTION OF THE STRATA FOR FEEDING THE FLAME FRONT AND FORCING THE FLAME FRONT DOWNWARDLY AROUND THE WELL 